Abrasive particles, method of making abrasive particles, and abrasive articles

ABSTRACT

Shaped ceramic abrasive particles include a first surface having a perimeter having a perimeter comprising at least first and second edges. A first region of the perimeter includes the second edge and extends inwardly and terminates at two corners defining first and second acute interior angles. The perimeter has at most four corners that define acute interior angles. A second surface is disposed opposite, and not contacting, the first surface. A peripheral surface is disposed between and connects the first and second surfaces. The peripheral surface has a first predetermined shape. Methods of making the shaped ceramic abrasive particles, and abrasive articles including them are also disclosed.

FIELD

The present disclosure broadly relates to abrasive particles, abrasivearticles, and methods of making and using the same.

BACKGROUND

In recent years, shaped abrasive particles produced by molding asol-gel, drying, and sintering the dried sol-gel to obtain a shapedceramic abrasive particle have gained popularity in the abrasivesindustry. Diamond turning techniques are commonly used to make suitablemolds, especially those for producing fine grades of abrasive particles,but have been limited in terms of the shapes of mold cavities that canbe produced.

SUMMARY

The present inventor has discovered that by lessening the angle formedat peripheral corners of shaped ceramic abrasive particles, improvedabrasive properties can be achieved.

Shaped abrasive particles, in general, can have superior performanceover randomly crushed abrasive particles. By controlling the shape ofthe abrasive particle it is possible to control the resultingperformance of the abrasive article. The inventor has discovered that bymaking at least one edge of shaped abrasive particles inwardlyextending, adjacent corners are typically sharpened, leading tounexpected improvement in abrading performance.

In one aspect, the present disclosure provides a shaped ceramic abrasiveparticle comprising:

-   -   a first surface having a perimeter comprising at least first and        second edges, wherein a first region of the perimeter comprises        the second edge and extends inwardly and terminates at two        corners defining first and second acute interior angles, and        wherein the perimeter has at most four corners that define acute        interior angles;    -   a second surface opposite, and not contacting, the first        surface; and    -   a peripheral surface disposed between and connecting the first        and second surfaces, wherein the peripheral surface comprises a        first wall that contacts the perimeter at the first edge,        wherein the peripheral surface comprises a second wall that        contacts the perimeter at the second edge, and wherein the        peripheral surface has a first predetermined shape.

In another aspect, the present disclosure provides a plurality ofabrasive particles, wherein the plurality of abrasive particlescomprises, on a numerical basis, at least 10, 20, 30, 40, 50, 60, 70,80, 90, 95, or even at least 99 percent of the shaped ceramic abrasiveparticles according to the present disclosure.

Abrasive particles according to the present disclosure are useful, forexample, in manufacture and use of abrasive articles.

In yet another aspect, the present disclosure provides abrasive articlescomprising shaped ceramic abrasive particles according to the presentdisclosure retained in a binder.

The present inventors have also developed methods enabling themanufacturing of shaped ceramic abrasive particles (including finegrades) according to the present disclosure.

Accordingly, in yet another aspect, the present disclosure provides amethod of making shaped ceramic abrasive particles, the methodcomprising steps:

a) providing a mold defining a mold cavity, wherein the mold cavity hasan outer opening defined by a perimeter, wherein the perimeter comprisesat least the first and second edges, wherein a first region of theperimeter comprises the second edge and extends inwardly and terminatesat two corners defining first and second acute interior angles, andwherein the perimeter has at most four corners that define acuteinterior angles, and wherein the mold cavity is laterally bounded by aperipheral mold surface comprising a first mold wall that intersects theperimeter at the first edge and a second mold wall that intersects theperimeter at the second edge;

b) disposing a ceramic precursor material within the mold cavity;

c) converting the ceramic precursor material disposed within the moldcavity into a shaped ceramic precursor particle; and

d) converting the shaped ceramic precursor particle into the shapedceramic abrasive particle.

In some embodiments, the method further comprises separating the shapedceramic precursor particle from the mold prior to step d). In someembodiments, step d) comprises sintering the shaped ceramic precursorparticle. In some embodiments, step d) comprises calcining the shapedceramic precursor particle to provide a calcined shaped ceramicprecursor particle, and sintering the calcined shaped ceramic precursorparticle.

The following definitions apply throughout the specification and claims.

The term “angle” is defined hereinbelow, for example, in reference toFIGS. 6A-6D.

The term “calcining” refers to removal volatile matter (e.g., freewater) from a ceramic precursor by heating at lower temperatureconditions than typically used for sintering.

The term “ceramic abrasive particle” refers to an abrasive particlecomprising ceramic material.

The term “corner” refers to the place, position, or angle formed by themeeting of two converging lines or edges. A corner may be sharp as,e.g., a point or edge. A corner may also be a generally rounded regionconnecting adjacent lines or faces.

The term “draft angle” refers to an angle of taper, incorporated into awall of a mold cavity so that the opening of the mold cavity is widerthan its base. Referring now to FIG. 1, which shows a cross-section ofmold 100 and mold cavity 105, draft angle μ is the angle between moldbase 150 and mold wall 130. The draft angle can be varied to change therelative sizes of the first and second surfaces and the sides of theperipheral surface. In various embodiments of the present disclosure,the draft angle μ can be 90 degrees or in a range of from about 95degrees to about 130 degrees, from about 95 degrees to about 125degrees, from about 95 degrees to about 120 degrees, from about 95degrees to about 115 degrees, from about 95 degrees to about 110degrees, from about 95 degrees to about 105 degrees, or from about 95degrees to about 100 degrees. As used herein, the term draft angle alsorefers to the angle of taper of walls of a molded body corresponding tothe draft angle of the mold used to produce it. For example, a draftangle of the exemplary shaped ceramic abrasive particle 300 in FIG. 3would be the angle between second surface 370 and wall 384.

The term “face” refers to a substantially planar surface, which maycomprise minor imperfections, for example, as arising duringmanufacture.

The term “interior angle” refers to an angle, within the perimeter,defined by two adjacent edges of the perimeter.

The term “length” refers to the maximum extent of an object along itsgreatest dimension.

The term “major surface” refers to a surface that is larger than atleast half of the surfaces in the object being referenced.

The term “perimeter” refers to a closed boundary of a surface, which maybe a planar surface, or a non-planar surface.

The term “predetermined shape” means that the shape is replicated from amold cavity used during making of the ceramic abrasive particle. Theterm “predetermined shape” excludes random shapes obtained by amechanical crushing operation.

The term “sintering” refers a process in which heating of a ceramicprecursor material causes it to undergo substantial transformation to acorresponding ceramic material.

The term “thickness” refers to the maximum extent of something along adimension orthogonal to both the length and the width.

The term “width” refers to the maximum extent of something along adimension orthogonal to the length.

The features and advantages of the present disclosure will be furtherunderstood upon consideration of the detailed description as well as theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional edge view of an exemplary moldshowing how to determine a draft angle.

FIG. 2 is a schematic perspective view of an exemplary shaped ceramicabrasive particle according to the present disclosure.

FIG. 3 is a schematic perspective view of an exemplary shaped ceramicabrasive particle according to the present disclosure.

FIG. 4 is a schematic perspective view of another exemplary shapedceramic abrasive particle according to the present disclosure.

FIGS. 5A-5C are schematic top views of other exemplary shaped ceramicabrasive particles according to the present disclosure.

FIGS. 6A-6D are schematic top views of various corners showing how tocalculate their angle.

FIG. 7 is a schematic cutaway perspective view of an exemplary molduseful in making shaped ceramic abrasive particles according to thepresent disclosure.

FIG. 8 is a cross-sectional edge view of an exemplary coated abrasivearticle according to the present disclosure.

FIG. 9 is a perspective view of a bonded abrasive article according tothe present disclosure.

FIG. 10 is an enlarged side view of a nonwoven abrasive articleaccording to the present disclosure.

FIG. 11 is a photomicrograph of shaped ceramic abrasive particles SAP1.

FIG. 12 is a photomicrograph of shaped alumina abrasive particles SAPA,prepared according to the disclosure of paragraph [0128] of U.S. Pat.Appln. Publ. No. 2010/0146867 (Boden et al.) using a draft angle of 98degrees.

FIGS. 13 and 14 are plots comparing cut rate and cumulative cut forabrasive discs of Example 1 and Comparative Examples A and B.

FIG. 15 is a photomicrograph of shaped ceramic abrasive particles SAP2.

FIG. 16 is a photomicrograph of shaped ceramic abrasive particles SAP3.

FIG. 17 is a plot comparing the performance of discs made with particlesfrom Example 1, Example 2, Example 3, and Comparative Example C on 1045Carbon Steel.

FIG. 18 is a plot comparing the performance of discs of Example 4,Example 5, Example 6, and Comparative Example D when used to abrade 304Stainless Steel.

FIG. 19 is a plot comparing of the performance of discs of Example 4,Example 5, Example 6, and Comparative Example D.

FIG. 20A is a photomicrograph of shaped alumina abrasive particles SAPB,prepared according to the disclosure of U.S. Pat. No. 8,142,531 (Adefriset al.).

FIG. 20B is a photomicrograph of shaped ceramic abrasive particles SAP4.

FIG. 21 is a plot comparing the performance of discs of Example 7,Comparative Example E and Comparative Example F.

FIGS. 22 and 23 are plots comparing the performance of discs of Example8 and Comparative Example G when used to abrade 1045 carbon steel and304 Stainless Steel, respectively.

While the above-identified drawing figures set forth several embodimentsof the present disclosure, other embodiments are also contemplated; forexample, as noted in the discussion. In all cases, the disclosure ispresented by way of representation and not limitation. It should beunderstood that numerous other modifications and embodiments can bedevised by those skilled in the art, which fall within the scope andspirit of the principles of the disclosure. The figures may not be drawnto scale. Like reference numbers may have been used throughout thefigures to denote like parts.

DETAILED DESCRIPTION

Referring now to FIG. 2, exemplary shaped ceramic abrasive particle 200comprises first surface 210 having perimeter 220. Second surface 270 isopposite, and does not contact first surface 210. Peripheral surface 280has a predetermined shape, and is disposed between and connects firstand second major surfaces 210, 270. Perimeter 220 comprises first andsecond edges 230, 232. Peripheral surface 280 comprises first and secondwalls 282, 284. First and second edges 230, 232 respectively representthe intersection of first and second walls 282, 284 with perimeter 220.First region 290 of perimeter 220 comprises first edge 230 and extendsinwardly and terminates at first and second corners 250, 252 definingrespective acute interior angles 260, 262.

In some embodiments, an inwardly extending region of a shaped ceramicabrasive particle according to the present disclosure may have a maximumdepth that is at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, oreven 60 percent of the maximum dimension of the shaped ceramic abrasiveparticle parallel to the maximum depth. For example, reference is madeto FIG. 2, which shows maximum dimension 218 parallel to maximum depth215. Similarly, in FIG. 3, maximum dimension 318 is parallel to maximumdepth 315.

In the embodiment shown in FIG. 2, first surface 210 has a firstpredetermined shape that corresponds to the base of a mold cavity usedto form it. However, if mold having two opposed openings is used (e.g.,as in the case of a perforated plate), neither of the first or secondmajor surfaces may have a predetermined shape, while the peripheralsurface will.

In some embodiments, shaped ceramic abrasive particles according to thepresent disclosure have a peripheral surface that includes at leastthree walls. Referring now to FIG. 3, exemplary shaped ceramic abrasiveparticle 300 comprises first surface 310 having perimeter 320. Perimeter320 comprises first, second, and third edges 330, 332, 334. First edge330 is a concave monotonic curve, while second and third edges 332, 334are substantially straight edges. Second surface 370 is opposite, anddoes not contact, first major surface 310. Peripheral surface 380 has apredetermined shape, and is disposed between and connects first andsecond surfaces 310, 370. Peripheral surface 380 comprises first,second, and third walls 382, 384, 386. First, second, and third edges330, 332, 334 respectively represent the intersection of first, second,and third walls 382, 384, 386 with perimeter 320. First region 390 ofperimeter 320 comprises inwardly extending first edge 330, andterminates at first and second corners 350, 352 defining respectivefirst and second acute interior angles 360, 362.

As shown in FIGS. 2 and 3, the first region of the perimeter maycomprise a single curved inwardly extending edge, however it is alsocontemplated that the first region of the perimeter may comprisemultiple edges (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10 edges, or more).

Referring now to FIG. 4, exemplary shaped ceramic abrasive particle 400comprises first surface 410 having perimeter 420. Perimeter 420comprises first, second, third, and fourth substantially straight edges430, 432, 434, 436. Second surface 470 is opposite, and does notcontact, first surface 410. Peripheral surface 480 comprises first,second, third, and fourth walls 482, 484, 486, 488. Peripheral surface480 has a predetermined shape, and is disposed between and connectsfirst and second major surfaces 410, 470. First, second, third, andfourth edges 430, 432, 434, 436 respectively represent the intersectionof first, second, third, and fourth walls 482, 484, 486, and 488 withperimeter 420. First region 490 of perimeter 420 comprises first edge430 and fourth edge 436, and extends inwardly. First region 490terminates at first and second corners 450, 452 defining respectivefirst and second acute interior angles 460, 462.

FIGS. 3 and 4 depict shaped ceramic abrasive particles that haveperimeters that are arrowhead-shaped. Likewise, in some embodiments, theshaped ceramic abrasive particles themselves may be arrowhead shaped.

In some embodiments, more than one region and/or edge of the perimetermay be inwardly extending. For example, referring now to FIG. 5A,exemplary shaped ceramic abrasive particle 500 a has perimeter 520 a offirst surface 510 a with two inwardly extending regions 590 a, 592 aformed by edges 530 a, 532 a and each terminating at two of acutecorners 550 a, 552 a, 554 a. Referring now to FIG. 5B, exemplary shapedceramic abrasive particle 500 b has perimeter 520 b of first surface 510b with three inwardly extending regions 590 b, 592 b, 594 b formed byedges 530 b, 532 b, 534 b and each terminating at two of acute corners550 b, 552 b, 554 b. Likewise, referring now to FIG. 5C, exemplaryshaped ceramic abrasive particle 500 c of first surface 510 c hasperimeter 520 c with four inwardly extending regions 590 c, 592 c, 594c, 596 c formed by edges 530 c, 532 c, 534 c, 536 c at each terminatingat two corners 550 c, 552 c, 554 c, 556 c defining acute interior angles(not shown).

By definition, the perimeter of the first major surface, except for anyinwardly extending regions, extends outwardly. For example, theperimeter may be outwardly extending except for one, two, three, or fourinwardly extending regions. Inwardly extending region(s) of theperimeter may comprise, for example, single curved edge(s) (e.g.,monotonic curved edge(s)), or multiple curved or substantially straight(e.g., linear) edges, or a combination of curved and substantiallystraight edges.

Typically, shaped ceramic abrasive particles according to the presentdisclosure have thicknesses that are substantially less than theirlength and/or width, although this is not a requirement. For example,the thickness of shaped ceramic abrasive particle may be less than orequal to one-third, one-fifth, or one-tenth of its length and/or width.

Generally, the first and second surfaces are substantially parallel, oreven parallel; however, this is not a requirement. For example, randomdeviations due to drying may result in one or both of the first andsecond major surfaces being non planar. Likewise, the first and/orsecond major surface may have parallel grooves formed therein, forexample, as described in U.S. Pat. Appln. Publ. No. 2010/0146867 A1(Boden et al.).

Shaped ceramic abrasive particles according to the present disclosurecomprise ceramic material. In some embodiments, they may consistessentially of ceramic material or even consist of ceramic material,although they may contain non-ceramic phases (e.g., as in aglass-ceramic). Examples of suitable ceramic materials include alphaalumina, fused alumina-zirconia, and fused oxynitrides. Further detailsconcerning sol-gel derived ceramic materials suitable for use in shapedceramic abrasive particles according to the present disclosure can befound in, for example, U.S. Pat. No. 4,314,827 (Leitheiser et al.); U.S.Pat. No. 4,518,397 (Leitheiser et al.); U.S. Pat. No. 4,623,364(Cottringer et al.); U.S. Pat. No. 4,744,802 (Schwabel); U.S. Pat. No.4,770,671 (Monroe et al.); U.S. Pat. No. 4,881,951 (Wood et al.); U.S.Pat. No. 4,960,441 (Pellow et al.); U.S. Pat. No. 5,139,978 (Wood); U.S.Pat. No. 5,201,916 (Berg et al.); U.S. Pat. No. 5,366,523 (Rowenhorst etal.); U.S. Pat. No. 5,429,647 (Larmie); U.S. Pat. No. 5,547,479 (Conwellet al.); U.S. Pat. No. 5,498,269 (Larmie); U.S. Pat. No. 5,551,963(Larmie); U.S. Pat. No. 5,725,162 (Garg et al.), and U.S. Pat. No.6,054,093 (Torre et al.).

In order to facilitate removal from a mold used to make them, andtypically to increase performance in abrading applications, shapedceramic abrasive particles according to the present disclosure may betapered corresponding a draft angle of the mold, for example, asdescribed in U.S. Pat. Appln. Publ. No. 2010/0151196 A1 (Adefris etal.). In other embodiments, the peripheral surface may not taper (i.e.,it may be vertical), and/or the first and second surfaces may have thesame size and shape.

In some embodiments, interior angles formed between the inwardlyextending region and either or both adjacent edges of the perimeter aresmaller than would be the case if the inwardly extending region wasreplaced, for example, by a single straight line segment or a convexedge. For example, in the case of an equilateral triangle, all cornershave an interior angle of 60 degrees, while for corresponding shapeshaving a concave edge replacing one of the triangle's edges according toone embodiment of the present disclosure, the interior angles of the twocorners adjacent to the inwardly extending region may be substantiallyreduced. For example, in the case of generally triangular shaped ceramicabrasive particles the interior angles may be in a range of from 5, 10,15, 20, 25, or 30 degrees up to 35, 40, 45, 50, or 55 degrees, or from40 to 55 degrees. In some embodiments, the interior angles may be in arange of from 35 to 55 degrees, from 40 to 55 degrees, or even from 45to 55 degrees, although other values are also possible. Similarly, iftwo (or three) of the triangle's edges are replaced with inwardlyextending curved edges, the interior angles of their adjacent cornersmay fall in the same range or be even lower. The same trend occurs inthe case of perimeters having four or more edges, although the interiorangle values may tend to be larger.

In order to measure the interior angle (θ) of a corner of the perimeter,one takes the angle formed between the tangents (T₁, T₂) of respectiveedges forming the corner at their closest point to the corner that hasnot passed an inflection point with respect to the inwardly extendingregion. In the case of intersecting straight edges (e.g., as shown inFIG. 6A), tangents T_(1a) and T_(2a) have the same slope as the edgesthemselves and the interior angle can be easily determined. In the casewhere one or both or the edges are monotonic inwardly extending curves(e.g., as shown in FIGS. 6B and 6C), the tangents (T_(1b) and T_(2b) orT_(1c) and T_(2c)), respectively) can likewise be readily determined byapproaching the corner along the curved edge(s). However, if the corneris round or otherwise deformed (e.g., as shown in FIG. 6D), themeasurement of the interior angle of the corner could become moreproblematic. Accordingly, in such cases, the tangents T_(1d) and T_(2d))should be determined by measuring the tangent of each adjacent edge asthey approach the inflection points (if present) proximate to thecorner, shown as P₁ and P₂ in FIG. 6D.

Shaped ceramic abrasive particles according to the present disclosureare typically used as a plurality of particles that may include theshaped ceramic abrasive particles of the present disclosure, othershaped abrasive particles, and/or crushed abrasive particles. Forexample, a plurality of abrasive particles according to the presentdisclosure may comprise, on a numerical basis, at least 10, 20, 30, 40,50, 60, 70, 80, 90, 95, or even 99 percent, or more percent of shapedceramic abrasive particles described herein. The shaped ceramic abrasiveparticles may have the same nominal size and shape, although in someembodiments, it may be useful to use a combination of sizes and/orshapes.

Typically, shaped ceramic abrasive particles according to the presentdisclosure have a relatively small maximum particle dimension; forexample, less than about 1 centimeter (cm), 5 millimeters (mm), 2 mm, 1mm, 200 micrometers, 100 micrometers, 50 micrometers, 20 micrometers, 10micrometers, or even less than 5 micrometers, although other sizes maybe used.

Any of the abrasive particles referred to in the present disclosure maybe sized according to an abrasives industry recognized specified nominalgrade. Exemplary abrasive industry recognized grading standards includethose promulgated by ANSI (American National Standards Institute), FEPA(Federation of European Producers of Abrasives), and JIS (JapaneseIndustrial Standard). Such industry accepted grading standards include,for example: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 30, ANSI 36,ANSI 40, ANSI 50, ANSI 60, ANSI 80, ANSI 100, ANSI 120, ANSI 150, ANSI180, ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400, andANSI 600; FEPA P8, FEPA P12, FEPA P16, FEPA P24, FEPA P30, FEPA P36,FEPA P40, FEPA P50, FEPA P60, FEPA P80, FEPA P100, FEPA P120, FEPA P150,FEPA P180, FEPA P220, FEPA P320, FEPA P400, FEPA P500, FEPA P600, FEPAP800, FEPA P1000, and FEPA P1200; and JIS 8, JIS 12, JIS 16, JIS 24, JIS36, JIS 46, JIS 54, JIS 60, JIS 80, JIS 100, JIS 150, JIS 180, JIS 220,JIS 240, JIS 280, JIS 320, JIS 360, JIS 400, JIS 400, JIS 600, JIS 800,JIS 1000, JIS 1500, JIS 2500, JIS 4000, JIS 6000, JIS 8000, and JIS10,000. More typically, the shaped ceramic abrasive particles areindependently sized to ANSI 60 and 80 or FEPA P60 and P80 gradingstandards.

The term “abrasives industry recognized specified nominal grade” alsoincludes abrasives industry recognized specified nominal screenedgrades. For example, specified nominal screened grades may use U.S.A.Standard Test Sieves conforming to ASTM E-11-09 “Standard Specificationfor Wire Cloth and Sieves for Testing Purposes.” ASTM E-11-09 sets forthrequirements for the design and construction of testing sieves using amedium of woven wire cloth mounted in a frame for the classification ofmaterials according to a designated particle size. A typical designationmay be represented as −18+20, meaning that the shaped ceramic abrasiveparticles pass through a test sieve meeting ASTM E11-09 “StandardSpecification for Woven Wire Test Sieve Cloth and Test Sieves”specifications for the number 18 sieve and are retained on a test sievemeeting ASTM E11-09 specifications for the number 20 sieve. In oneembodiment, the shaped ceramic abrasive particles have a particle sizesuch that at least 90 percent of the particles pass through an 18 meshtest sieve and can be retained on a 20, 25, 30, 35, 40, 45, or 50 meshtest sieve. In various embodiments, the shaped ceramic abrasiveparticles can have a nominal screened grade comprising: −18+20, −20/+25,−25+30, −30+35, −35+40, 5−40+45, −45+50, −50+60, −60+70, −70/+80,−80+100, −100+120, −120+140, −140+170, −170+200, −200+230, −230+270,−270+325, −325+400, −400+450, −450+500, or −500+635.

In some embodiments, shaped ceramic abrasive particles can be madeaccording to a multistep process. The process can be carried out using aceramic precursor dispersion (e.g., a dispersion (e.g., a sol-gel)comprising a ceramic precursor material).

Briefly, the method comprises the steps of making either a seeded ornon-seeded ceramic precursor dispersion that can be converted into acorresponding ceramic (e.g., a boehmite sol-gel that can be converted toalpha alumina); filling one or more mold cavities having the desiredouter shape of the shaped abrasive particle with a ceramic precursordispersion, drying the ceramic precursor dispersion to form shapedceramic precursor particles; removing the shaped ceramic precursorparticles from the mold cavities; calcining the shaped ceramic precursorparticles to form calcined, shaped ceramic precursor particles, and thensintering the calcined, shaped ceramic precursor particles to formshaped ceramic abrasive particles.

In some embodiments, the calcining step is omitted and the shapedceramic precursor particles are sintered directly after removal from themold. In some embodiments, the mold may be made of a sacrificialmaterial (e.g., a polyolefin material) that is burned off duringcalcining or sintering, thereby eliminating to separate the ceramicprecursor particles from it during processing.

The process will now be described in greater detail in the context ofalpha-alumina-containing shaped ceramic abrasive particles.

The first process step involves providing either a seeded or non-seededdispersion of a ceramic precursor material (i.e., a ceramic precursordispersion) that can be converted into a ceramic material. The ceramicprecursor dispersion often comprises a volatile liquid component. In oneembodiment, the volatile liquid component is water. The ceramicprecursor dispersion should comprise a sufficient amount of liquid forthe viscosity of the dispersion to be sufficiently low to enable fillingmold cavities and replicating the mold surfaces, but not so much liquidas to cause subsequent removal of the liquid from the mold cavity to beprohibitively expensive. In one embodiment, the ceramic precursordispersion comprises from 2 to 90 percent by weight of the particlesthat can be converted into ceramic, such as particles of aluminum oxidemonohydrate (boehmite) or another alumina precursor, and at least 10 to98 percent by weight, or from 50 to 70 percent by weight, or 50 to 60percent by weight, of the volatile component such as water. Conversely,the ceramic precursor dispersion in some embodiments contains from 30 to50 percent, or 40 to 50 percent by weight solids.

Examples of useful ceramic precursor dispersions include zirconium oxidesols, vanadium oxide sols, cerium oxide sols, aluminum oxide sols, andcombinations thereof. Useful aluminum oxide dispersions include, forexample, boehmite dispersions and other aluminum oxide hydratesdispersions. Boehmite can be prepared by known techniques or can beobtained commercially. Examples of commercially available boehmiteinclude products having the trade designations “DISPERAL”, and “DISPAL”,both available from Sasol North America, Inc. or “HIQ-40” available fromBASF Corporation. These aluminum oxide monohydrates are relatively pure;that is, they include relatively little, if any, hydrate phases otherthan monohydrates, and have a high surface area.

The physical properties of the resulting shaped ceramic abrasiveparticles will generally depend upon the type of material used in theceramic precursor dispersion. As used herein, a “gel” is a threedimensional network of solids dispersed in a liquid.

The ceramic precursor dispersion may contain a modifying additive orprecursor of a modifying additive. The modifying additive can functionto enhance some desirable property of the abrasive particles or increasethe effectiveness of the subsequent sintering step. Modifying additivesor precursors of modifying additives can be in the form of solublesalts, typically water soluble salts. They typically consist of ametal-containing compound and can be a precursor of oxide of magnesium,zinc, iron, silicon, cobalt, nickel, zirconium, hafnium, chromium,yttrium, praseodymium, samarium, ytterbium, neodymium, lanthanum,gadolinium, cerium, dysprosium, erbium, titanium, and mixtures thereof.The particular concentrations of these additives that can be present inthe ceramic precursor dispersion can be varied based on skill in theart.

Typically, the introduction of a modifying additive or precursor of amodifying additive will cause the ceramic precursor dispersion to gel.The ceramic precursor dispersion can also be induced to gel byapplication of heat over a period of time to reduce the liquid contentin the dispersion through evaporation. The ceramic precursor dispersioncan also contain a nucleating agent. Nucleating agents suitable for thisdisclosure can include fine particles of alpha alumina, alpha ferricoxide or its precursor, titanium oxides and titanates, chrome oxides, orany other material that will nucleate the transformation. The amount ofnucleating agent, if used, should be sufficient to effect thetransformation of alpha alumina Nucleating alpha alumina precursordispersions is disclosed in U.S. Pat. No. 4,744,802 (Schwabel).

A peptizing agent can be added to the ceramic precursor dispersion toproduce a more stable hydrosol or colloidal ceramic precursordispersion. Suitable peptizing agents are monoprotic acids or acidcompounds such as acetic acid, hydrochloric acid, formic acid, andnitric acid. Multiprotic acids can also be used but they can rapidly gelthe ceramic precursor dispersion, making it difficult to handle or tointroduce additional components thereto. Some commercial sources ofboehmite contain an acid titer (such as absorbed formic or nitric acid)that will assist in forming a stable ceramic precursor dispersion.

The ceramic precursor dispersion can be formed by any suitable means;for example, in the case of a sol-gel alumina precursor by simply mixingaluminum oxide monohydrate with water containing a peptizing agent or byforming an aluminum oxide monohydrate slurry to which the peptizingagent is added.

Defoamers or other suitable chemicals can be added to reduce thetendency to form bubbles or entrain air while mixing. Additionalchemicals such as wetting agents, alcohols, or coupling agents can beadded if desired.

The second process step involves providing a mold having at least onemold cavity, and preferably a plurality of cavities formed in at leastone major surface of the mold.

Referring now to FIG. 7, exemplary mold 700 defines mold cavity 795.Mold cavity 795 is laterally bounded by peripheral mold surface 780comprising first, second, and third mold walls 782, 784, 786. Moldcavity 795 has outer opening 797 defined by a perimeter 720. First moldwall 782 intersects perimeter 720 at first edge 730. Second mold wall784 intersects perimeter 720 at second edge 732. First region 790 ofperimeter 720 extends inwardly and comprises first edge 730, whichterminates at first and second corners 750, 752, which define respectivefirst and second acute interior angles 760, 762.

In some embodiments, the mold is formed as a production tool, which canbe, for example, a belt, a sheet, a continuous web, a coating roll suchas a rotogravure roll, a sleeve mounted on a coating roll, or a die. Inone embodiment, the production tool comprises polymeric material.Examples of suitable polymeric materials include thermoplastics such aspolyesters, polycarbonates, poly(ether sulfone), poly(methylmethacrylate), polyurethanes, polyvinylchloride, polyolefin,polystyrene, polypropylene, polyethylene or combinations thereof, orthermosetting materials. In one embodiment, the entire tooling is madefrom a polymeric or thermoplastic material. In another embodiment, thesurfaces of the tooling in contact with the ceramic precursor dispersionwhile drying, such as the surfaces of the plurality of cavities,comprises polymeric or thermoplastic materials and other portions of thetooling can be made from other materials. A suitable polymeric coatingmay be applied to a metal tooling to change its surface tensionproperties by way of example.

A polymeric or thermoplastic production tool can be replicated off ametal master tool. The master tool will have the inverse pattern desiredfor the production tool. The master tool can be made in the same manneras the production tool. In one embodiment, the master tool is made outof metal, e.g., nickel and is diamond turned. In one embodiment, themaster tool is at least partially formed using stereolithography. Thepolymeric sheet material can be heated along with the master tool suchthat the polymeric material is embossed with the master tool pattern bypressing the two together. A polymeric or thermoplastic material canalso be extruded or cast onto the master tool and then pressed. Thethermoplastic material is cooled to solidify and produce the productiontool. If a thermoplastic production tool is utilized, then care shouldbe taken not to generate excessive heat that may distort thethermoplastic production tool limiting its life. More informationconcerning the design and fabrication of production tooling or mastertools can be found in U.S. Pat. No. 5,152,917 (Pieper et al.); U.S. Pat.No. 5,435,816 (Spurgeon et al.); U.S. Pat. No. 5,672,097 (Hoopman etal.); U.S. Pat. No. 5,946,991 (Hoopman et al.); U.S. Pat. No. 5,975,987(Hoopman et al.); and U.S. Pat. No. 6,129,540 (Hoopman et al.).

Access to cavities can be from an opening in the top surface or bottomsurface of the mold. In some instances, the cavities can extend for theentire thickness of the mold. Alternatively, the cavities can extendonly for a portion of the thickness of the mold. In one embodiment, thetop surface is substantially parallel to bottom surface of the mold withthe cavities having a substantially uniform depth. At least one edge ofthe mold, that is, the edge in which the cavities are formed, can remainexposed to the surrounding atmosphere during the step in which thevolatile component is removed.

The cavities have a specified three-dimensional shape to make the shapedceramic abrasive particles. The depth dimension is equal to theperpendicular distance from the top surface to the lowermost point onthe bottom surface. The depth of a given cavity can be uniform or canvary along its length and/or width. The cavities of a given mold can beof the same shape or of different shapes.

The third process step involves filling the cavities in the mold withthe ceramic precursor dispersion (e.g., by a conventional technique). Insome embodiments, a knife roll coater or vacuum slot die coater can beused. A mold release can be used to aid in removing the particles fromthe mold if desired. Typical mold release agents include oils such aspeanut oil or mineral oil, fish oil, silicones, polytetrafluoroethylene,zinc stearate, and graphite. In general, mold release agent such aspeanut oil, in a liquid, such as water or alcohol, is applied to thesurfaces of the production tooling in contact with the ceramic precursordispersion such that between about 0.1 mg/in² (0.02 mg/cm²) to about 3.0mg/in² (0.5 mg/cm²), or between about 0.1 mg/in² (0.02 mg/cm²) to about5.0 mg/in² (0.8 mg/cm²) of the mold release agent is present per unitarea of the mold when a mold release is desired. In some embodiments,the top surface of the mold is coated with the ceramic precursordispersion. The ceramic precursor dispersion can be pumped onto the topsurface.

Next, a scraper or leveler bar (i.e., a screed) can be used to force theceramic precursor dispersion fully into the cavity of the mold. Theremaining portion of the ceramic precursor dispersion that does notenter cavity can be removed from top surface of the mold and recycled.In some embodiments, a small portion of the ceramic precursor dispersioncan remain on the top surface and in other embodiments the top surfaceis substantially free of the dispersion. The pressure applied by thescraper or leveler bar is typically less than 100 psi (0.7 MPa), lessthan 50 psi (0.3 MPa), or even less than 10 psi (69 kPa). In someembodiments, no exposed surface of the ceramic precursor dispersionextends substantially beyond the top surface.

In those embodiments, wherein it is desired to have the exposed surfacesof the cavities result in substantially planar faces of the shapedceramic abrasive particles, it may be desirable to overfill the cavities(e.g., using a micronozzle array) and slowly dry the ceramic precursordispersion.

The fourth process step involves removing the volatile component to drythe dispersion. Desirably, the volatile component is removed by fastevaporation rates. In some embodiments, removal of the volatilecomponent by evaporation occurs at temperatures above the boiling pointof the volatile component. An upper limit to the drying temperatureoften depends on the material the mold is made from. For polypropylenetooling the temperature should be less than the melting point of theplastic. In one embodiment, for a water dispersion of between about 40to 50 percent solids and a polypropylene mold, the drying temperaturescan be between about 90° C. to about 165° C., or between about 105° C.to about 150° C., or between about 105° C. to about 120° C. Highertemperatures can lead to improved production speeds but can also lead todegradation of the polypropylene tooling limiting its useful life as amold.

The fifth process step involves removing resultant shaped ceramicprecursor particles from the mold cavities. The shaped ceramic precursorparticles can be removed from the cavities by using the followingprocesses alone or in combination on the mold: gravity, vibration,ultrasonic vibration, vacuum, or pressurized air to remove the particlesfrom the mold cavities.

The shaped ceramic precursor particles can be further dried outside ofthe mold. If the ceramic precursor dispersion is dried to the desiredlevel in the mold, this additional drying step is not necessary.However, in some instances it may be economical to employ thisadditional drying step to minimize the time that the ceramic precursordispersion resides in the mold. Typically, the shaped ceramic precursorparticles will be dried from 10 to 480 minutes, or from 120 to 400minutes, at a temperature from 50° C. to 160° C., or at 120° C. to 150°C.

The sixth process step involves calcining the shaped ceramic precursorparticles. During calcining, essentially all the volatile material isremoved, and the various components that were present in the ceramicprecursor dispersion are transformed into metal oxides. The shapedceramic precursor particles are generally heated to a temperature from400° C. to 800° C., and maintained within this temperature range untilthe free water and over 90 percent by weight of any bound volatilematerial are removed. In an optional step, it may be desired tointroduce the modifying additive by an impregnation process. Awater-soluble salt can be introduced by impregnation into the pores ofthe calcined, shaped ceramic precursor particles. Then the shapedceramic precursor particles are pre-fired again. This option is furtherdescribed in U.S. Pat. No. 5,164,348 (Wood).

The seventh process step involves sintering the calcined, shaped ceramicprecursor particles to form ceramic particles. Prior to sintering, thecalcined, shaped ceramic precursor particles are not completelydensified and thus lack the desired hardness to be used as shapedceramic abrasive particles. Sintering takes place by heating thecalcined, shaped ceramic precursor particles to a temperature of from1000° C. to 1650° C. The length of time to which the calcined, shapedceramic precursor particles must be exposed to the sintering temperatureto achieve this level of conversion depends upon various factors butusually from five seconds to 48 hours is typical.

In another embodiment, the duration for the sintering step ranges fromone minute to 90 minutes. After sintering, the shaped ceramic abrasiveparticles can have a Vickers hardness of 10 GPa (gigapascals), 16 GPa,18 GPa, 20 GPa, or greater.

Other steps can be used to modify the described process such as, forexample, rapidly heating the material from the calcining temperature tothe sintering temperature, centrifuging the ceramic precursor dispersionto remove sludge and/or waste. Moreover, the process can be modified bycombining two or more of the process steps if desired. Conventionalprocess steps that can be used to modify the process of this disclosureare more fully described in U.S. Pat. No. 4,314,827 (Leitheiser).

Shaped ceramic abrasive particles composed of crystallites of alphaalumina, magnesium alumina spinel, and a rare earth hexagonal aluminatemay be prepared using sol-gel alpha alumina precursor particlesaccording to methods described in, for example, U.S. Pat. No. 5,213,591(Celikkaya et al.) and U.S. Publ. Pat. Appl. Nos. 2009/0165394 A1(Culler et al.) and 2009/0169816 A1 (Erickson et al.). Alpha aluminaabrasive particles may contain zirconia as disclosed in U.S. Pat. No.5,551,963 (Larmie). Alternatively, alpha alumina abrasive particles mayhave a microstructure or additives, for example, as disclosed in U.S.Pat. No. 6,277,161 (Castro). More information concerning methods to makeshaped ceramic abrasive particles is disclosed in co-pending U.S. Publ.Patent Appln. No. 2009/0165394 A1 (Culler et al.).

Surface coatings on the shaped ceramic abrasive particles may be used toimprove the adhesion between the shaped ceramic abrasive particles and abinder material in abrasive articles, or can be used to aid inelectrostatic deposition of the shaped ceramic abrasive particles. Inone embodiment, surface coatings as described in U.S. Pat. No. 5,352,254(Celikkaya) in an amount of 0.1 to 2 percent surface coating to shapedabrasive particle weight may be used. Such surface coatings aredescribed in U.S. Pat. No. 5,213,591 (Celikkaya et al.); U.S. Pat. No.5,011,508 (Wald et al.); U.S. Pat. No. 1,910,444 (Nicholson); U.S. Pat.No. 3,041,156 (Rowse et al.); U.S. Pat. No. 5,009,675 (Kunz et al.);U.S. Pat. No. 5,085,671 (Martin et al.); U.S. Pat. No. 4,997,461(Markhoff-Matheny et al.); and U.S. Pat. No. 5,042,991 (Kunz et al.).Additionally, the surface coating may prevent the shaped abrasiveparticle from capping. Capping is the term to describe the phenomenonwhere metal particles from the workpiece being abraded become welded tothe tops of the shaped ceramic abrasive particles. Surface coatings toperform the above functions are known to those of skill in the art.

The shaped ceramic abrasive particles of the present disclosure cantypically be made using tools (or molds that are inverse replicasthereof) cut using diamond tooling, which provides higher featuredefinition than other fabrication alternatives such as, for example,stamping or punching. Typically, the cavities in the tool surface havesmooth faces that meet along sharp edges, although this is not arequirement. The resultant shaped ceramic abrasive particles have arespective nominal average shape that corresponds to the shape ofcavities in the tool surface; however, variations (e.g., randomvariations) from the nominal average shape may occur during manufacture,and shaped ceramic abrasive particles exhibiting such variations areincluded within the definition of shaped ceramic abrasive particles asused herein.

Shaped ceramic abrasive particles are useful, for example, in theconstruction of abrasive articles, including for example, agglomerateabrasive grain, coated abrasive articles (for example, conventional makeand size coated abrasive articles, slurry coated abrasive articles, andstructured abrasive articles), abrasive brushes, nonwoven abrasivearticles, and bonded abrasive articles such as grinding wheels, honesand whetstones. In general, abrasive articles comprise a plurality ofabrasive particles retained in a binder.

Coated abrasive articles generally include a backing, abrasiveparticles, and at least one binder to secure the abrasive particles tothe backing. The backing can be any suitable material, including cloth,polymeric film, fiber, nonwoven webs, paper, combinations thereof, andtreated versions thereof. Suitable binders include inorganic or organicbinders (including thermally curable resins and radiation curableresins). The abrasive particles can be present in one layer or in twolayers of the coated abrasive article.

An example of a coated abrasive article is depicted in FIG. 8. Referringto FIG. 8, exemplary coated abrasive article 800 has a backing(substrate) 802 and abrasive layer 803. Abrasive layer 803 includesshaped ceramic abrasive particles 804 secured to a major surface ofbacking 802 by make layer 805 and size layer 806. In some instances, asupersize coat (not shown) is used.

Bonded abrasive articles typically include a shaped mass of abrasiveparticles held together by an organic, metallic, or vitrified binder.Such shaped mass can be, for example, in the form of a wheel, such as agrinding wheel or cutoff wheel. The diameter of grinding wheelstypically is about 1 cm to over 1 meter; the diameter of cut off wheelsabout 1 cm to over 80 cm (more typically 3 cm to about 50 cm). The cutoff wheel thickness is typically about 0.5 mm to about 5 cm, moretypically about 0.5 mm to about 2 cm. The shaped mass can also be in theform, for example, of a honing stone, segment, mounted point, disc (e.g.double disc grinder) or other conventional bonded abrasive shape. Bondedabrasive articles typically comprise about 3-50 percent by volume bondmaterial, about 30-90 percent by volume abrasive particles (or abrasiveparticle blends), up to 50 percent by volume additives (includinggrinding aids), and up to 70 percent by volume pores, based on the totalvolume of the bonded abrasive article.

An exemplary grinding wheel is shown in FIG. 9. Referring to FIG. 9,exemplary grinding wheel 900 is depicted, which includes shaped ceramicabrasive particles 911 according to the present disclosure, molded in awheel and mounted on hub 912.

Nonwoven abrasive articles typically include an open porous loftypolymer filament structure having shaped ceramic abrasive particles madeaccording to the present disclosure distributed throughout the structureand adherently bonded therein by an organic binder. Examples offilaments include polyester fibers, polyamide fibers, and polyaramidfibers. An exemplary nonwoven abrasive article is shown in FIG. 10.Referring to FIG. 10, a schematic depiction, greatly enlarged, of atypical nonwoven abrasive article 1000 is shown, comprises lofty openfibrous mat 1050 as a substrate, onto which shaped ceramic abrasiveparticles made according to the present disclosure 1052 are adhered bybinder 1054.

Useful abrasive brushes include those having a plurality of bristlesunitary with a backing (see, e.g., U.S. Pat. No. 5,427,595 (Pihl etal.), U.S. Pat. No. 5,443,906 (Pihl et al.), U.S. Pat. No. 5,679,067(Johnson et al.), and U.S. Pat. No. 5,903,951 (Ionta et al.)).Desirably, such brushes are made by injection molding a mixture ofpolymer and abrasive particles.

Suitable organic binders for making abrasive articles includethermosetting organic polymers. Examples of suitable thermosettingorganic polymers include phenolic resins, urea-formaldehyde resins,melamine-formaldehyde resins, urethane resins, acrylate resins,polyester resins, aminoplast resins having pendant α,β-unsaturatedcarbonyl groups, epoxy resins, acrylated urethane, acrylated epoxies,and combinations thereof. The binder and/or abrasive article may alsoinclude additives such as fibers, lubricants, wetting agents,thixotropic materials, surfactants, pigments, dyes, antistatic agents(e.g., carbon black, vanadium oxide, or graphite), coupling agents(e.g., silanes, titanates or zircoaluminates), plasticizers, suspendingagents. The amounts of these optional additives are selected to providethe desired properties. The coupling agents can improve adhesion to theabrasive particles and/or filler. The binder chemistry may be thermallycured, radiation cured or combinations thereof. Additional details onbinder chemistry may be found in U.S. Pat. No. 4,588,419 (Caul et al.),U.S. Pat. No. 4,751,138 (Tumey et al.), and U.S. Pat. No. 5,436,063(Follett et al.).

More specifically with regard to vitrified bonded abrasives, vitreousbonding materials, which exhibit an amorphous structure and aretypically hard, are well known in the art. In some cases, the vitreousbonding material includes crystalline phases. Bonded, vitrified abrasivearticles made according to the present disclosure may be in the shape ofa wheel (including cut off wheels), honing stone, mounted points orother conventional bonded abrasive shape. In some embodiments, avitrified bonded abrasive article made according to the presentdisclosure is in the form of a grinding wheel.

Examples of metal oxides that are used to form vitreous bondingmaterials include: silica, silicates, alumina, soda, calcia, potassia,titania, iron oxide, zinc oxide, lithium oxide, magnesia, boria,aluminum silicate, borosilicate glass, lithium aluminum silicate,combinations thereof. Typically, vitreous bonding materials can beformed from composition comprising from 10 to 100 percent glass frit,although more typically the composition comprises 20 to 80 percent glassfrit, or 30 to 70 percent glass frit. The remaining portion of thevitreous bonding material can be a non-frit material. Alternatively, thevitreous bond may be derived from a non-frit containing composition.Vitreous bonding materials are typically matured at a temperature(s) ina range of about 700° C. to about 1500° C., usually in a range of about800° C. to about 1300° C., sometimes in a range of about 900° C. toabout 1200° C., or even in a range of about 950° C. to about 1100° C.The actual temperature at which the bond is matured depends, forexample, on the particular bond chemistry.

In some embodiments, vitrified bonding materials include thosecomprising silica, alumina (desirably, at least 10 percent by weightalumina), and boria (desirably, at least 10 percent by weight boria). Inmost cases the vitrified bonding material further comprises alkali metaloxide(s) (e.g., Na₂O and K₂O) (in some cases at least 10 percent byweight alkali metal oxide(s)).

Binder materials may also contain filler materials or grinding aids,typically in the form of a particulate material. Typically, theparticulate materials are inorganic materials. Examples of usefulfillers for this disclosure include: metal carbonates (e.g., calciumcarbonate (e.g., chalk, calcite, marl, travertine, marble andlimestone), calcium magnesium carbonate, sodium carbonate, magnesiumcarbonate), silica (e.g., quartz, glass beads, glass bubbles and glassfibers) silicates (e.g., talc, clays, (montmorillonite) feldspar, mica,calcium silicate, calcium metasilicate, sodium aluminosilicate, sodiumsilicate) metal sulfates (e.g., calcium sulfate, barium sulfate, sodiumsulfate, aluminum sodium sulfate, aluminum sulfate), gypsum,vermiculite, wood flour, aluminum trihydrate, carbon black, metal oxides(e.g., calcium oxide (lime), aluminum oxide, titanium dioxide), andmetal sulfites (e.g., calcium sulfite).

In general, the addition of a grinding aid increases the useful life ofthe abrasive article. A grinding aid is a material that has asignificant effect on the chemical and physical processes of abrading,which results in improved performance Although not wanting to be boundby theory, it is believed that a grinding aid(s) will (a) decrease thefriction between the abrasive particles and the workpiece being abraded,(b) prevent the abrasive particles from “capping” (i.e., prevent metalparticles from becoming welded to the tops of the abrasive particles),or at least reduce the tendency of abrasive particles to cap, (c)decrease the interface temperature between the abrasive particles andthe workpiece, or (d) decreases the grinding forces.

Grinding aids encompass a wide variety of different materials and can beinorganic or organic based. Examples of chemical groups of grinding aidsinclude waxes, organic halide compounds, halide salts and metals andtheir alloys. The organic halide compounds will typically break downduring abrading and release a halogen acid or a gaseous halide compound.Examples of such materials include chlorinated waxes liketetrachloronaphthalene, pentachloronaphthalene, and polyvinyl chloride.Examples of halide salts include sodium chloride, potassium cryolite,sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodiumtetrafluoroborate, silicon fluorides, potassium chloride, and magnesiumchloride. Examples of metals include, tin, lead, bismuth, cobalt,antimony, cadmium, and iron titanium. Other miscellaneous grinding aidsinclude sulfur, organic sulfur compounds, graphite, and metallicsulfides. It is also within the scope of the present disclosure to use acombination of different grinding aids, and in some instances this mayproduce a synergistic effect.

Grinding aids can be particularly useful in coated abrasive and bondedabrasive articles. In coated abrasive articles, grinding aid istypically used in the supersize coat, which is applied over the surfaceof the abrasive particles. Sometimes, however, the grinding aid is addedto the size coat. Typically, the amount of grinding aid incorporatedinto coated abrasive articles are about 50-300 g/m² (desirably, about80-160 g/m²). In vitrified bonded abrasive articles grinding aid istypically impregnated into the pores of the article.

The abrasive articles can contain 100 percent shaped ceramic abrasiveparticles made according to the present disclosure, or blends of suchabrasive particles with other abrasive particles and/or diluentparticles. However, at least about 2 percent by weight, desirably atleast about 5 percent by weight, and more desirably about 30-100 percentby weight, of the abrasive particles in the abrasive articles should beshaped ceramic abrasive particles made according to the presentdisclosure. In some instances, the abrasive particles made according tothe present disclosure may be blended with other abrasive particlesand/or diluent particles at a ratio between 5 to 75 percent by weight,about 25 to 75 percent by weight about 40 to 60 percent by weight, orabout 50 to 55 percent by weight (i.e., in equal amounts by weight).Examples of suitable conventional abrasive particles include fusedaluminum oxide (including white fused alumina, heat-treated aluminumoxide and brown aluminum oxide), silicon carbide, boron carbide,titanium carbide, diamond, cubic boron nitride, garnet, fusedalumina-zirconia, and sol-gel-derived abrasive particles. In someinstances, blends of abrasive particles may result in an abrasivearticle that exhibits improved grinding performance in comparison withabrasive articles comprising 100 percent of either type of abrasiveparticle.

Examples of suitable diluent particles include marble, gypsum, flint,silica, iron oxide, aluminum silicate, glass (including glass bubblesand glass beads), alumina bubbles, alumina beads and diluentagglomerates.

The abrasive particles may be uniformly distributed in the abrasivearticle or concentrated in selected areas or portions of the abrasivearticle. For example, in a coated abrasive, there may be two layers ofabrasive particles. The first layer comprises abrasive particles otherthan shaped ceramic abrasive particles made according to the presentdisclosure, and the second (outermost) layer comprises shaped ceramicabrasive particles made according to the present disclosure. Likewise ina bonded abrasive, there may be two distinct sections of the grindingwheel. The outermost section may comprise abrasive particles madeaccording to the present disclosure, whereas the innermost section doesnot. Alternatively, shaped ceramic abrasive particles made according tothe present disclosure may be uniformly distributed throughout thebonded abrasive article.

Further details regarding coated abrasive articles can be found, forexample, in U.S. Pat. No. 4,734,104 (Broberg), U.S. Pat. No. 4,737,163(Larkey), U.S. Pat. No. 5,203,884 (Buchanan et al.), U.S. Pat. No.5,152,917 (Pieper et al.), U.S. Pat. No. 5,378,251 (Culler et al.), U.S.Pat. No. 5,417,726 (Stout et al.), U.S. Pat. No. 5,436,063 (Follett etal.), U.S. Pat. No. 5,496,386 (Broberg et al.), U.S. Pat. No. 5,609,706(Benedict et al.), U.S. Pat. No. 5,520,711 (Helmin), U.S. Pat. No.5,954,844 (Law et al.), U.S. Pat. No. 5,961,674 (Gagliardi et al.), andU.S. Pat. No. 5,975,988 (Christianson). Further details regarding bondedabrasive articles can be found, for example, in U.S. Pat. No. 4,543,107(Rue), U.S. Pat. No. 4,741,743 (Narayanan et al.), U.S. Pat. No.4,800,685 (Haynes et al.), U.S. Pat. No. 4,898,597 (Hay et al.), U.S.Pat. No. 4,997,461 (Markhoff-Matheny et al.), U.S. Pat. No. 5,037,453(Narayanan et al.), U.S. Pat. No. 5,110,332 (Narayanan et al.), and U.S.Pat. No. 5,863,308 (Qi et al.). Further details regarding vitreousbonded abrasives can be found, for example, in U.S. Pat. No. 4,543,107(Rue), U.S. Pat. No. 4,898,597 (Hay et al.), U.S. Pat. No. 4,997,461(Markhoff-Matheny et al.), U.S. Pat. No. 5,094,672 (Giles Jr. et al.),U.S. Pat. No. 5,118,326 (Sheldon et al.), U.S. Pat. No. 5,131,926(Sheldon et al.), U.S. Pat. No. 5,203,886 (Sheldon et al.), U.S. Pat.No. 5,282,875 (Wood et al.), U.S. Pat. No. 5,738,696 (Wu et al.), andU.S. Pat. No. 5,863,308 (Qi). Further details regarding nonwovenabrasive articles can be found, for example, in U.S. Pat. No. 2,958,593(Hoover et al.).

The present disclosure provides a method of abrading a surface, themethod comprising contacting at least one shaped ceramic abrasiveparticle made according to the present disclosure, with a surface of aworkpiece; and moving at least of one the shaped ceramic abrasiveparticles or the contacted surface to abrade at least a portion of saidsurface with the abrasive particle. Methods for abrading with shapedceramic abrasive particles made according to the present disclosurerange from snagging (i.e., high pressure high stock removal) topolishing (e.g., polishing medical implants with coated abrasive belts),wherein the latter is typically done with finer grades (e.g., ANSI 220and finer) of abrasive particles. The shaped ceramic abrasive particlesmay also be used in precision abrading applications, such as grindingcam shafts with vitrified bonded wheels. The size of the abrasiveparticles used for a particular abrading application will be apparent tothose skilled in the art.

Abrading with shaped ceramic abrasive particles made according to thepresent disclosure may be done dry or wet. For wet abrading, the liquidmay be introduced supplied in the form of a light mist to completeflood. Examples of commonly used liquids include: water, water-solubleoil, organic lubricant, and emulsions. The liquid may serve to reducethe heat associated with abrading and/or act as a lubricant. The liquidmay contain minor amounts of additives such as bactericide, antifoamingagents.

Shaped ceramic abrasive particles made according to the presentdisclosure may be useful, for example, to abrade workpieces such asaluminum metal, carbon steels, mild steels, tool steels, stainlesssteel, hardened steel, titanium, glass, ceramics, wood, wood-likematerials (e.g., plywood and particle board), paint, painted surfaces,organic coated surfaces and the like. The applied force during abradingtypically ranges from about 1 to about 100 kilograms.

Select Embodiments of the Present Disclosure

In embodiment 1, the present disclosure provides a shaped ceramicabrasive particle comprising:

-   -   a first surface having a perimeter comprising at least first and        second edges, wherein a first region of the perimeter comprises        the second edge and extends inwardly and terminates at two        corners defining first and second acute interior angles, and        wherein the perimeter has at most four corners that define acute        interior angles;    -   a second surface opposite, and not contacting, the first        surface; and    -   a peripheral surface disposed between and connecting the first        and second surfaces, wherein the peripheral surface comprises a        first wall that contacts the perimeter at the first edge,        wherein the peripheral surface comprises a second wall that        contacts the perimeter at the second edge, and wherein the        peripheral surface has a first predetermined shape.

In embodiment 2, the present disclosure provides a shaped ceramicabrasive particle according to embodiment 1, wherein the second surfacehas a second predetermined shape.

In embodiment 3, the present disclosure provides a shaped ceramicabrasive particle according to embodiment 1 or 2, wherein the secondsurface has the same shape as the first surface.

In embodiment 4, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 3, whereinthe first acute interior angle is in a range of from 5 to 55 degrees,inclusive.

In embodiment 5, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 4, whereinthe peripheral surface comprises a third wall that contacts the firstsurface at a third edge, wherein the first region of the perimeterfurther comprises the third edge, and wherein at least one of the secondedge or the third edge is substantially straight.

In embodiment 6, the present disclosure provides a shaped ceramicabrasive particle according to embodiment 5, wherein the first and thirdedges are substantially straight.

In embodiment 7, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 4 to 6, whereinthe peripheral surface consists of the first, second, and third walls.

In embodiment 8, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 4 to 7, whereinthe peripheral surface further comprises a fourth wall that intersectsthe perimeter at a fourth edge.

In embodiment 9, the present disclosure provides a shaped ceramicabrasive particle according to embodiment 8, wherein the first, second,third, and fourth edges are inwardly extending.

In embodiment 10, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 9, whereinthe second edge is a monotonic concave curve.

In embodiment 11, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 10, whereinthe shaped ceramic abrasive particle has a thickness that is less thanor equal to one-third of its width.

In embodiment 12, the present disclosure provides a shaped ceramicabrasive particle according to embodiment 11, and wherein the secondacute interior angle is in a range of from 5 to 55 degrees, inclusive

In embodiment 13, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 12, whereinthe shaped ceramic abrasive particle has a length of less than or equalto one centimeter.

In embodiment 14, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 13, whereinthe shaped ceramic abrasive particles consist essentially of ceramicmaterial.

In embodiment 15, the present disclosure provides a shaped ceramicabrasive particle according to embodiment 14, wherein the ceramicmaterial comprises alpha alumina.

In embodiment 16, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 15, whereinthe first and second surfaces are substantially parallel.

In embodiment 17, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 16, whereinthe peripheral surface slopes inwardly from the first surface toward thesecond surface.

In embodiment 18, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 17, whereinthe peripheral surface slopes have a draft angle in a range of from 92to 105 degrees, inclusive.

In embodiment 19, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 18, whereinthe first surface is larger than the second surface.

In embodiment 20, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 19, whereinthe first region of the perimeter is a monotonic curve.

In embodiment 21, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 20, whereinthe perimeter the first edge is substantially straight and the secondedge is curved.

In embodiment 22, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 21, whereinthe perimeter first edge is substantially straight and the second edgeis curved.

In embodiment 23, the present disclosure provides a shaped ceramicabrasive particle according to any one of embodiments 1 to 22, whereinthe perimeter is arrowhead-shaped.

In embodiment 24, the present disclosure provides a plurality ofabrasive particles, wherein the plurality of abrasive particlescomprises, on a numerical basis, at least 10 percent of shaped ceramicabrasive particles according to any one of embodiments 1 to 23.

In embodiment 25, the present disclosure provides a plurality ofabrasive particles, wherein the plurality of abrasive particlescomprises, on a numerical basis, at least 30 percent of shaped ceramicabrasive particles according to any one of embodiments 1 to 23.

In embodiment 26, the present disclosure provides a plurality ofabrasive particles, wherein the plurality of abrasive particlescomprises, on a numerical basis, at least 50 percent of shaped ceramicabrasive particles according to any one of embodiments 1 to 23.

In embodiment 27, the present disclosure provides a plurality ofabrasive particles, wherein the plurality of abrasive particlescomprises, on a numerical basis, at least 70 percent of shaped ceramicabrasive particles according to any one of embodiments 1 to 23.

In embodiment 28, the present disclosure provides a plurality ofabrasive particles according to any one of embodiments 24 to 27, furthercomprising crushed abrasive particles.

In embodiment 29, the present disclosure provides an abrasive articlecomprising a plurality of abrasive particles according to any one ofembodiments 24 to 28 retained in a binder.

In embodiment 30, the present disclosure provides an abrasive articleaccording to embodiment 29, wherein the abrasive article comprises abonded abrasive article.

In embodiment 31, the present disclosure provides an abrasive articleaccording to embodiment 30, wherein the bonded abrasive articlecomprises a bonded abrasive wheel.

In embodiment 32, the present disclosure provides an abrasive articleaccording to embodiment 29, wherein the abrasive article comprises acoated abrasive article, the coated abrasive article comprising theplurality of abrasive particles secured to a backing having third andfourth opposed major surfaces.

In embodiment 33, the present disclosure provides an abrasive articleaccording to embodiment 29, wherein the abrasive article comprises anonwoven abrasive article, wherein the nonwoven abrasive articlecomprises the plurality of abrasive particles secured to a lofty opennonwoven fiber web.

In embodiment 34, the present disclosure provides a method of makingshaped ceramic abrasive particles, the method comprising steps:

a) providing a mold defining a mold cavity, wherein the mold cavity hasan outer opening defined by a perimeter, wherein the perimeter comprisesat least the first and second edges, wherein a first region of theperimeter comprises the second edge and extends inwardly and terminatesat two corners defining first and second acute interior angles, andwherein the perimeter has at most four corners that define acuteinterior angles, and wherein the mold cavity is laterally bounded by aperipheral mold surface comprising a first mold wall that intersects theperimeter at the first edge and a second mold wall that intersects theperimeter at the second edge;

b) disposing a ceramic precursor material within the mold cavity;

c) converting the ceramic precursor material disposed within the moldcavity into a shaped ceramic precursor particle; and

d) converting the shaped ceramic precursor particle into the shapedceramic abrasive particle.

In embodiment 35, the present disclosure provides a method according toembodiment 34, wherein the first corner has a first acute interior anglewith a value in a range of from 5 to 55 degrees, inclusive

In embodiment 36, the present disclosure provides a method according toembodiment 34 or 35, wherein the mold comprises an open mold.

In embodiment 37, the present disclosure provides a method according toembodiment 34 or 35, wherein the mold further comprises a bottom moldsurface in contact with the first and second mold walls.

In embodiment 38, the present disclosure provides a method according toany one of embodiments 34 to 37, wherein the mold cavity has a depth,and wherein the first and second walls slope inwardly with increasingdepth.

In embodiment 39, the present disclosure provides a method according toany one of embodiments 34 to 38, wherein the second edge comprises acurved edge.

In embodiment 40, the present disclosure provides a method according toany one of embodiments 34 to 39, wherein the first region of theperimeter is a monotonic curve.

In embodiment 41, the present disclosure provides a method according toany one of embodiments 34 to 40, wherein the perimeter comprises atleast one substantially straight edge and at least one curved edge.

In embodiment 42, the present disclosure provides a method according toany one of embodiments 34 to 41, wherein the perimeter comprises atleast two substantially straight edges and a curved edge.

In embodiment 43, the present disclosure provides a method according toany one of embodiments 34 to 42, wherein the perimeter consists of twosubstantially straight edges and a curved edge.

In embodiment 44, the present disclosure provides a method according toany one of embodiments 34 to 42, wherein the peripheral mold surfacefurther comprises a third mold wall, and wherein the third mold wallintersects the perimeter at a third edge.

In embodiment 45, the present disclosure provides a method according toembodiment 44, wherein the third edge extends inwardly with respect tothe perimeter.

In embodiment 46, the present disclosure provides a method according toany one of embodiments 34 to 45, wherein the perimeter isarrowhead-shaped.

In embodiment 47, the present disclosure provides a method according toany one of embodiments 34 to 46, wherein the perimeter comprises atleast two substantially straight edges.

In embodiment 48, the present disclosure provides a method according toembodiment 47, wherein the peripheral surface further comprises a fourthmold wall, and wherein the fourth mold wall intersects the perimeter ata fourth edge.

In embodiment 49, the present disclosure provides a method according toany one of embodiments 34 to 48, wherein the method further comprisesseparating the shaped ceramic precursor particle from the mold prior tostep d).

In embodiment 50, the present disclosure provides a method according toembodiment 49, wherein step d) comprises sintering the shaped ceramicprecursor particle.

In embodiment 51, the present disclosure provides a method according toembodiment 49, wherein step d) comprises calcining the shaped ceramicprecursor particle to provide a calcined shaped ceramic precursorparticle, and sintering the calcined shaped ceramic precursor particle.

In embodiment 52, the present disclosure provides a method according toany one of embodiments 34 to 51, wherein the shaped ceramic abrasiveparticle comprises alpha alumina.

In embodiment 53, the present disclosure provides a method according toany one of embodiments 34 to 52, wherein the ceramic precursor materialcomprises a sol-gel.

In embodiment 54, the present disclosure provides a method according toany one of embodiments 34 to 53, wherein the ceramic precursor materialcomprises an alpha alumina precursor.

In embodiment 55, the present disclosure provides a method according toany one of embodiments 34 to 54, wherein each mold cavity has a maximumlateral dimension of less than or equal to one centimeter.

In embodiment 56, the present disclosure provides a method according toany one of embodiments 34 to 55, wherein each of the shaped ceramicabrasive particles has a thickness that is less than or equal toone-third of its width.

Objects and advantages of this disclosure are further illustrated by thefollowing non-limiting examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this disclosure.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in theExamples and the rest of the specification are by weight.

Preparation of Shaped Ceramic Abrasive Particles

A sample of boehmite sol-gel was made using the following recipe:aluminum oxide monohydrate powder (1600 parts) available as DISPERALfrom Sasol North America, Inc. was dispersed by high shear mixing in asolution containing water (2400 parts) and 70 aqueous nitric acid (72parts) for 11 minutes. The resulting sol-gel was aged for at least 1hour before coating. The sol-gel was forced into production toolinghaving shaped mold cavities of dimensions reported in Table 1 (below),wherein “NA” means not applicable. SAPA shaped alumina particles wereprepared according to the disclosure of paragraph [0128] of U.S. Pat.Appln. Publ. No. 2010/0146867 (Boden et al.) using a draft angle of 98degrees. Shaped Ceramic Abrasive Particles of the same general shape andcomposition as SAPB were prepared according to the disclosure of U.S.Pat. No. 8,142,531 (Adefris et al.)

TABLE 1 MAXIMUM INTERSECTION SHAPED STRAIGHT NUMBER OF ANGLE WITHCERAMIC SHAPE, EDGE INWARDLY INWARDLY DRAFT ANGLE ABRASIVEREPRESENTATIVE LENGTH, EXTENDING EXTENDING ON ALL EDGES, PARTICLE MEDIANPARTICLE FIGURE mm EDGES EDGE, degrees degrees THICKNESS, mm SAP1triangular, 2.8 1 30 8 0.71 FIG. 11 SAP2 triangular, 3.8 1 45 8 0.71FIG. 15 SAP3 triangular, 2.8 1 25 8 0.71 FIG. 16 SAP4 square, 2.8 4 60 80.71 FIG. 20B SAP5 triangular, 1.3 1 30 8 0.33 smaller scale version ofSAP1 SAPA triangular, 2.8 0 NA 8 0.71 FIG. 12 using a draft angle of 98degrees SAPB square, 2.8 0 NA 8 0.71 FIG. 20A SAPC triangular 1.3 0 NA 80.33 smaller scale version of SAPA

A mold release agent, 1 percent peanut oil in methanol, was used withabout 0.5 mg/in² (0.08 mg/cm²) of peanut oil applied to the productiontooling having an array of mold cavities. The excess methanol wasremoved by placing sheets of the production tooling in an air convectionoven for 5 minutes at 45° C. The sol-gel was forced into the cavitieswith a putty knife so that the openings of the production tooling werecompletely filled. The sol-gel coated production tooling was placed inan air convection oven at 45° C. for at least 45 minutes to dry. Theshaped ceramic precursor particles were removed from the productiontooling by passing it over an ultrasonic horn. The shaped ceramicprecursor particles were calcined at approximately 650° C. and thensaturated with a with a mixed nitrate solution of MgO, Y₂O₃, CoO, andLa₂O₃.

All of the shaped ceramic abrasive particles described in the Exampleswere treated to enhance electrostatic application of the shaped ceramicabrasive particles in a manner similar to the method used to makecrushed abrasive particles disclosed in U.S. Pat. No. 5,352,254(Celikkaya). The calcined, precursor shaped ceramic abrasive particleswere impregnated with a rare earth oxide (REO) solution comprising 1.4percent MgO, 1.7 percent Y₂O₃, 5.7 percent La₂O₃ and 0.07 percent CoO.Into 70 grams of the REO solution, 1.4 grams of HYDRAL COAT 5 0.5micrometer particle size aluminum trihydroxide powder available fromAlmatis of Leetsdale, Pa., was dispersed by stirring it in an openbeaker. About 100 grams of calcined, precursor shaped ceramic abrasiveparticles was then impregnated with the 71.4 grams of the HYDRAL COAT 5powder dispersion in REO solution. The impregnated, calcined, precursorshaped ceramic abrasive particles were allowed to dry after which theparticles were again calcined at 650° C. and sintered at approximately1400° C. to final hardness. Both the calcining and sintering werecarried out using rotary tube kilns under ambient atmosphere. Theresulting composition was an alumina composition containing 1 weightpercent MgO, 1.2 weight percent of Y₂O₃, 4 weight percent of La₂O₃ and0.05 weight percent of CoO, with traces of TiO₂, SiO₂, and CaO.

General Procedure for Preparing Abrasive Discs

Abrasive articles were prepared from the abrasive particles prepared asdescribed above and the coating compositions shown in Table 2. 7-inch(17.8 cm) diameter fiber discs with ⅞-inch (2.2-cm) diameter arbor holesof a vulcanized fiber backing having a thickness of 0.83 mm (33 mils)(obtained as DYNOS VULCANIZED FIBRE from DYNOS Gmbh, Troisdorf, Germany)were coated with 3.5 grams/disc of the make coat composition,electrostatically coated with 15.0 grams/disc of abrasive particles, andthen 13.0 grams/disc of the size coat composition was applied. All ofthe discs that were used to grind stainless steel samples were furthercoated with 10 grams of supersize coat after partially curing the discsat 90° C. for 90 minutes. Following curing at 102° C. for 10 hours, thediscs were flexed.

TABLE 2 PARTS BY WEIGHT SUPER- MATERIAL DESCRIPTION MAKE SIZE SIZEResole metal hydroxide 49.15 29.42 none phenolic catalyzed phenol- resinformaldehyde resin, ca. 75 percent in water Epoxy EPON 828 epoxy resinobtained none none 30.96 Resin from Momentive Specialty Chemicals,Columbus, Ohio Water Water 10.19 18.12 11.52 Filler calcium carbonatehaving a 40.56 none none particle size less than 46 micrometers and anaverage particle size of about 15 micrometers, obtained as GEORGIAMARBLE NO. 10 from Georgia Marble, Gantts Quarry, Alabama Grindingcryolite, obtained as RTN none 50.65 none aid Cryolite from TRInternational Trading Co., Houston, Texas Grinding Potassiumtetrafluoroborate none none 56.34 aid obtained from Solvay FluoridesLLC, Houston, Texas Surfactant 0.5 percent ethoxylated oleic  0.10  1.81none acid surfactant, obtained as EMULON A from BASF Corp., Mount Olive,New Jersey Surfactant AEROSOL OT-NV surfactant none none  0.78 obtainedfrom Cytec Industries, Woodland Park, New Jersey Curing IMICURE EMI 24curing none none  0.36 agent agent obtained from Air Products andChemicals, Allentown, Pennsylvania Anti-foam ANTIFOAM 1430 anti- nonenone  0.04 foaming agent obtained from Dow Corning Corporation, Midland,MichiganAbrasion Test

The abrasive discs were tested using the following procedure. Abrasivediscs (7-inch (17.8 cm) diameter) for evaluation were attached to arotary grinder fitted with a 7-inch (17.8 cm) ribbed disc pad face plate80514 EXTRA HARD RED, obtained from 3M Company, St. Paul, Minn.). Thegrinder was then activated and urged against an end face of a 0.75×0.75in (1.9×1.9 cm) pre-weighed 1045 carbon steel (or alternatively, 304stainless steel) bar under a load of 12 lb (4.5 kg). The rotationalspeed of the disc pad face plate under the above load condition againstthe workpiece was maintained at 5000 rpm. The workpiece was abradedunder these conditions for a total of fifty (50) 10-second grindingintervals (cycles). Following each 10-second cycle, the workpiece wasallowed to cool to room temperature and weighed to determine the cut ofthe abrasive operation. Test results were reported as cut rate,incremental cut, and/or cumulated cut vs. number of cycles.

Example 1 and Comparative Examples A-B

Example 1 and Comparative Examples A and B demonstrate the effect ofabrasive articles comprising the particles of the present disclosurewhen compared to abrasive articles comprising previously-known abrasiveparticles.

Example 1 was prepared according to the general procedure for preparingabrasive discs using SAP1 abrasive particles.

Comparative Example A was a 7-inch (17.8-cm) diameter fiber disc with a⅞ inch (2.2 cm) hole made with SAPA and is commercially available as“CUBITRON II FIBER DISC 982C, 36+” from 3M, Saint Paul, Minn.

Comparative Example B was a 7-inch (17.8-cm) diameter fiber disc with a⅞ inch (2.2 cm) hole made with conventionally crushed 3M CeramicAbrasive Grain and is commercially available as “988C” from 3M, SaintPaul, Minn.

Abrasive discs according to Example 1 and Comparative Examples A and Bwere tested according to the Abrasion Test. The comparative cut rate andcumulative cut data are shown in FIGS. 13 and 14, wherein the coatedabrasive of Example 1 exhibited cut that was at least 60 percent betterthan Comparative Example A (a comparable shaped ceramic abrasiveparticle with straight edges), and more than twice as good as comparablethe crushed ceramic grain of Comparative Example B.

Examples 2-6 and Comparative Example C

Examples 2-6 were prepared to compare with Example 1 to demonstrate theeffects of changing the intersecting angle created by a inwardlyextending edge with another edge.

Example 2 was prepared identically to Example 1 with the exception thatthe abrasive particles were SAP2 instead of SAP1.

Example 3 was prepared identically to Example 1 with the exception thatthe abrasive particles were SAP3 instead of SAP1.

Example 4 was prepared identically to Example 1 with the exception thata supersize coating was applied.

Example 5 was prepared identically to Example 2 with the exception thata supersize coating was applied.

Example 6 was prepared identically to Example 3 with the exception thata supersize coating was applied.

Comparative Example C was prepared identically to Example 1, with theexception that the abrasive particles were SAPA instead of SAP1.

Comparative Example D was prepared identically to Comparative Example C,with the exception that a supersize coating was applied.

Examples 1, 2, and 3 were tested according to the Abrasion Test. FIG. 17shows the comparison of the performance of discs made with particlesfrom Example 1, Example 2, Example 3, and Comparative Example C on 1045Carbon Steel. The initial cut rates of all the discs made with particleshaving and inwardly extending (concave) wall were higher than thosediscs made with particles with straight edges. The disc of Example 2performed the best. It maintained a higher cut rate throughout the test.

FIG. 18 shows the comparison of the performance of discs of Example 4,Example 5, Example 6, and Comparative Example D when used to abrade 304Stainless Steel. The initial cut rates of all the discs made withparticles that were supplied with concavities were higher than thosediscs made with conventional particles. Particularly the Example 6 discmade with SAP3 particles performed the best. It maintained higher cutrate than Comparative Example D as well as the other Example discsthroughout the test. This higher performance can be demonstrated betteras cumulative cut as a function of number of cycles as shown in FIG. 19.

Example 7 and Comparative Example E

Example 7 and Comparative Example E are abrasive articles thatdemonstrate the effects of an alternative embodiment of the inventiveparticle when compared to similar particles having straight edges, andalso with conventional crushed ceramic abrasive grain and iscommercially available as 321 3M Ceramic Abrasive Grain 321 from 3M,Saint Paul, Minn.

Example 7 was made identically to Example 1 with the exception that SAP4was substituted for SAP1.

Comparative Example E was made identically to Example 1 with theexception that SAPB was substituted for SAP1. Comparative Example F wasmade identically to Example 1 with the exception that “3M CeramicAbrasive Grain 321” (3M, Saint Paul, Minn.) was substituted for SAP1.

Example 7 and Comparative Examples E and F were tested according to theAbrasion Test on 1045 carbon steel. The test results are shown in FIG.21, again show that including an inwardly extending (e.g., concave)region in shaped ceramic abrasive particles transforms poorer-performingshaped particles into better-performing particles when compared toconventionally-crushed particles in abrasive disc articles.

Example 8 and Comparative Example G

Examples 8 and Comparative Example G demonstrate the effect of abrasivearticles comprising yet another embodiment of the particles of thepresent disclosure when compared to abrasive articles comprisingpreviously-known abrasive particles. Example 8 was prepared according tothe general procedure for preparing abrasive discs using SAP5 abrasiveparticles. Comparative Example G was prepared identically to Example 1with the exception that the abrasive particles were SAPC instead of SAP1and the discs were coated with 2.5 grams/disc of the make coatcomposition, electrostatically coated with 5.5 grams/disc of abrasiveparticles, and then 6.0 grams/disc of the size coat and 6.0 grams of thesupersize coat composition was applied.

Example 8 and Comparative Example G were tested according to theAbrasion Test on 1045 carbon steel and 304 stainless steel. Thecomparative cut rate data are shown in FIG. 22 for carbon steel and FIG.23 for stainless steel.

All patents and publications referred to herein are hereby incorporatedby reference in their entirety. All examples given herein are to beconsidered non-limiting unless otherwise indicated. Variousmodifications and alterations of this disclosure may be made by thoseskilled in the art without departing from the scope and spirit of thisdisclosure, and it should be understood that this disclosure is not tobe unduly limited to the illustrative embodiments set forth herein.

What is claim is:
 1. A shaped ceramic abrasive particle comprising: afirst surface having a perimeter comprising at least first and secondedges, wherein a first region of the perimeter comprises the second edgeand extends inwardly as a concave monotonic curve and terminates at twosharp corners defining first and second acute interior angles, whereinthe first acute interior angle is in the range of from 35 to 55 degrees,wherein the second acute interior angle is in the range of from 35 to 55degrees, wherein the first region of the perimeter has a maximum depththat is at least 5 percent of the maximum dimension of the shapedceramic abrasive particle parallel to the maximum depth, and wherein theperimeter has at most four corners that define acute interior angles; asecond surface opposite, and not contacting, the first surface; and aperipheral surface disposed between and connecting the first and secondsurfaces, wherein the peripheral surface comprises a first wall thatcontacts the perimeter at the first edge, wherein the peripheral surfacecomprises a second wall that contacts the perimeter at the second edge,and wherein the peripheral surface has a first predetermined shape. 2.The shaped ceramic abrasive particle of claim 1, wherein the shapedceramic abrasive particle has a thickness that is less than or equal toone-third of its width.
 3. The shaped ceramic abrasive particle of claim1, wherein the shaped ceramic abrasive particle consist essentially ofceramic material.
 4. The shaped ceramic abrasive particle of claim 1,wherein the first region of the perimeter has a maximum depth that is atleast 10 percent of the maximum dimension of the shaped ceramic abrasiveparticle parallel to the maximum depth.
 5. The shaped ceramic abrasiveparticle of claim 1, wherein the first region of the perimeter has amaximum depth that is at least 15 percent of the maximum dimension ofthe shaped ceramic abrasive particle parallel to the maximum depth. 6.The shaped ceramic abrasive particle of claim 1, wherein the firstregion of the perimeter has a maximum depth that is at least 20 percentof the maximum dimension of the shaped ceramic abrasive particleparallel to the maximum depth.
 7. The shaped ceramic abrasive particleof claim 1, wherein the first region of the perimeter has a maximumdepth that is at least 25 percent of the maximum dimension of the shapedceramic abrasive particle parallel to the maximum depth.
 8. The shapedceramic abrasive particle of claim 1, wherein the first region of theperimeter has a maximum depth that is at least 30 percent of the maximumdimension of the shaped ceramic abrasive particle parallel to themaximum depth.
 9. The shaped ceramic abrasive particle of claim 1,wherein the first region of the perimeter has a maximum depth that is atleast 35 percent of the maximum dimension of the shaped ceramic abrasiveparticle parallel to the maximum depth.
 10. The shaped ceramic abrasiveparticle of claim 1, wherein the first region of the perimeter has amaximum depth that is at least 40 percent of the maximum dimension ofthe shaped ceramic abrasive particle parallel to the maximum depth. 11.The shaped ceramic abrasive particle of claim 1, wherein the firstregion of the perimeter has a maximum depth that is at least 45 percentof the maximum dimension of the shaped ceramic abrasive particleparallel to the maximum depth.
 12. The shaped ceramic abrasive particleof claim 1, wherein the first region of the perimeter has a maximumdepth that is at least 50 percent of the maximum dimension of the shapedceramic abrasive particle parallel to the maximum depth.
 13. The shapedceramic abrasive particle of claim 1, wherein the first region of theperimeter has a maximum depth that is at least 55 percent of the maximumdimension of the shaped ceramic abrasive particle parallel to themaximum depth.
 14. The shaped ceramic abrasive particle of claim 1,wherein the first region of the perimeter has a maximum depth that is atleast 60 percent of the maximum dimension of the shaped ceramic abrasiveparticle parallel to the maximum depth.